1. Field of the Invention
The present invention relates to an extraction device capable of capturing and releasing objects from hollow bodies, and in particular, to a medical instrument for ensnaring and removing an object from a body.
2. Background of the Invention
Various instruments are known in the art for removing foreign objects from the body. For example, such instruments are used for removal of stones such as kidney stones, gallstones, and the like from various sites along the urinary tract of a patient's body. Retrieval devices are also widely used for removing foreign articles from the vascular system of a patient. In such a case, examples of the foreign articles include vena cava filters and parts of medical devices, such as catheters, guidewires, cardiac leads, etc., which may break and become detached during medical procedures.
Some types of these instruments employ a retrieval collapsible wire basket arranged within a flexible catheter formed as a tubular sheath adapted to penetrate body passages to reach the location where the object is to be evacuated. Another known type of the retrieval device is a snare configured as a single distal loop which is positioned over a free end of the foreign body, and which is collapsed and tightened around the foreign body.
In an attempt to provide a snare with improved cross sectional vessel coverage, multi loop snares have been developed. These snares include relatively free loops which are not joined at any point between the shaft and the distal ends of the loops. One drawback of many multi-loop snares is that the relative geometry of the free loops is difficult to maintain due to the lack of dilatative strength. These snares are not resistive to forces countering snare opening. Because the relative position of the loops can change, both within a catheter and within a body tract, the loops can actually become displaced and/or entangled, thus preventing the snare to be opened during operation.